1. Field of the Invention
The present invention relates to a data reproduction apparatus capable of controlling a reproduction time of encrypted data as a whole in decrypting and reproducing encrypted data obtained using a data distribution system that allows copyright protection for copied information, a data reproduction circuit for use therein, and a data recording apparatus.
2. Description of Related Art
By virtue of the progress in digital information communication networks and the like such as the Internet in these few years, each user can now easily access network information through individual-oriented terminals employing a mobile phone or the like.
In such digital information communication networks, information is transmitted through digital signals. It is now possible to obtain copied music data and video data transmitted via the aforementioned information communication network without degradation in the audio quality and picture quality of the copied information, even in the case where the copying operation is performed by an individual user.
Thus, there is a possibility of the copyright of the copyright owner being significantly infringed unless some appropriate measures to protect copyrights are taken when contents subject to copyright protection such as music and image data are to be transmitted on the digital information communication network.
However, if copyright protection is given top priority so that distribution of content data through the disseminating digital information communication network is suppressed, the copyright owner who can essentially collect a predetermined copyright royalty for copies of a copyrighted data will also incur some disbenefit.
To take an example of a recording medium with digital data recorded thereon, in stead of the distribution via a digital information communication network as described above, music data can be copied basically freely from a CD (compact disk) with commercially available music data recorded thereon to a magneto-optical disk (MD or the like) as long as the copied music is limited to private use. A private user who carries out digital recording or the like is supposed to indirectly pay a copy right owner a certain amount of the cost for a digital recorder itself, MD or the like as a deposit.
In view of the fact that music data copied from CD to MD is digital data that is hardly degraded when copied, a recording apparatus is configured to prohibit music data from being copied from a recordable MD to another MD as digital data for the purpose of copy right protection.
In this state of affairs, sufficient measures must be taken in distributing content data such as music and image data to the public through the digital information communication network for the purpose of copyright protection since distribution per se is an act subject to restriction based on the copyright owner's right of transmission to the public.
It is also necessary to prevent any unauthorized user from receiving content data transmitted to the public through a digital information communication network, as well as preventing any content data, once received by an authorized user, to be further copied without permission.
In view of the foregoing, a data distribution system through a digital communication network is proposed in which a distribution server storing encrypted content data that is an encrypted version of content data distributes the encrypted content data via a terminal device such as a mobile phone to a memory card loaded to the terminal device. In this data distribution system, a public encryption key of a memory card authenticated in advance by a certificate authority and a certificate thereof are transmitted to the distribution server when distribution of encrypted content data is requested. Upon confirming reception of the authorized certificate by the distribution server, the encrypted content data as well as the license key required to decrypt the encrypted content data are transmitted to the memory card. When the encrypted content data and the license key are transmitted, the distribution server and the memory card respectively generate session keys different from distribution to another distribution and encrypt public encryption keys using the generated session keys to exchange the keys between the distribution server and the memory card.
Eventually, the distribution server transmits to the memory card the license encrypted by an individual public encryption key for each memory card and further encrypted by the session key as well as encrypted content data. The memory card then records the received license key and encrypted content data into a memory.
To reproduce the encrypted content data recorded in the memory card, the user loads the memory card to a reproduction terminal with a dedicated reproduction circuit to reproduce the encrypted content data for enjoyment.
In such a system, a usage regulation provided to allow content suppliers or copyright owners to direct the usage for reproduction and copy of encrypted content data is distributed with a license key so that each apparatus can carry out processes according to the usage regulation.
The usage regulation includes a regulation for copy/transfer of licenses between memory cards, a regulation such as a limitation on the reproduction number of times when a license key is output from a memory card, and a regulation for handling reproduced content data.
The conventional system, however, is disadvantageous in that a safety operation is not ensured by defining a reproduction time as the usage regulation.
In other words, even if a reproduction time is defined as the usage regulation for handling reproduced content data, the operation does not work unless the regulation for a reproduction time recorded in a memory card keeps updated. Even if the system is configured to provide an updating instruction from a reproduction terminal to a memory card, the regulation for the reproduction time can be easily violated by interfering with transmittance of the updating instruction from the reproduction terminal to the memory card.